The German police have successfully deanonymized at least four Tor users. It appears they watch known Tor relays and known suspects, and use timing analysis to figure out who is using what relay.
Tor has written about this.
Hacker News thread.
—————
Free Unlimited, Encrypted, Anti Snoop & Ad Free Email
Boost Aviation Internet Speeds – Cuts tracking and Junk at source
Register UK names for just £2.99 a year
Check our Premium Domains and Freebies